1. Field of the Invention
The present invention relates to a fastener, and more particularly to a fastener used for mounting a heat-radiator to an electronic device on a circuit board.
2. Description of Prior Art
Electronic devices such as central processing units (CPUs) are the core administrator of electrical signals in most contemporary personal computers. Continued development of CPUs has enabled them to perform more and more functions. Heat generated by CPUs has increased commensurately. Such heat can adversely affect the operational stability of computers. Measures must be taken to efficiently remove the heat from the CPUs. Typically, a heat-radiator is mounted on a CPU to remove heat therefrom.
A number of conventional fasteners are used to mount the heat-radiator to the CPU. The fasteners extend through holes in the heat-radiator and the circuit board, and are constructed to exert a spring force that presses the heat-radiator against the CPU. As shown in FIG. 5, conventional fasteners 120 for mounting a heat-radiator 110 to a CPU 130 installed on a circuit board 140 are disclosed. The fastener 120 has a leg 122, a head 124 formed at a first end of the leg 122 and a cone-shaped foot 126 formed at a second end of the leg 122. The foot 126 has an engaging portion at a top thereof and an insertion end at a bottom thereof. Both the head 124 and the engaging portion of the foot 126 have a diameter larger than the leg 122, whereas the insertion portion of the foot 126 has a diameter smaller than the leg 122. A cylindrical spring 127 is located around a periphery of the leg 122 and between the head 124 and the foot 126. A channel 128 is longitudinally defined through the foot 126 and at least a portion of the leg 122 adjacent to the foot 126. Thus when the heat-radiator 110 is mounted, the foot 126 of the fastener 120 is squeezed to sequentially travel through corresponding holes in the heat-radiator 110 and the circuit board 140. After the engaging portion of the foot 126 extends the hole of the circuit board 140, the foot 126 recovers to its original state whereby the engaging portion of the foot 126 is engaged with an underside of the circuit board 140. At the same time, the spring 127 is pressed to push against a top surface of the heat-radiator 110. Thus the heat-radiator 110 is mounted on the CPU 130 for heat dissipation.
However, the fastener 120 is usually integrally made from plastic material by injection molding method. The engaging portion of the foot 126 of the fastener 120 has a tendency of wearing out during insertion action. The heat-resistance property of the fastener 120 is also not satisfactory. When used at a high temperature environment, the engaging portion of the foot 126 is prone to deform overly, and as a result, the heat-radiator 110 become loose or even dropped from the circuit board 140.
Therefore, it is desired to provide an improved fastener to obviate the aforementioned problems.